1. Field of the Invention
The invention relates to techniques of effecting an n-level quantization for a halftone multi-colored image decomposed into a plurality of pixels, for respective separate color-components contained in each pixel, and of forming ink dots using a plurality of different colored inks corresponding to the respective separate color-components, depending on the results of the n-level quantization.
The invention relates more particularly to techniques of effecting the n-level quantization for a subject pixel to reflect the tone levels of neighboring pixels of the subject pixel, to thereby suppress color bleed or spread between these pixels.
2. Description of the Related Art
There are known recording or printing devices of a color inkjet type. An example of such recording or printing devices is configured to perform a recording operation in which inks are jetted onto a recording sheet of paper, to thereby form the corresponding ink dots on the recording sheet. The inks each contain fine particles of separate colors: Cyan (C), Magenta (M), Yellow (Y), and Black (K).
It takes a few minutes before such an ink is dried and such fine particles of the ink are fixed to the recording sheet to form an ink dot, during which a solvent of the ink evaporates and penetrates into between fibers of the recording sheet.
The time required for the ink dot fixing (e.g., a drying time) is varied in length depending on the type of the ink used. For example, a pigment-based ink, which is harder to penetrate into between fibers of the recording sheet than a dye-based ink, requires a longer time to form an ink dot than the dye-based ink.
FIGS. 22A and 22B each schematically illustrate in enlargement a particle 100 of Y color ink and a particle 101 of K color ink with these being jetted onto a recording sheet at the respective positions adjacent to each other. FIG. 22A illustrates these particles 100, 101 in a state with the corresponding inks having been just jetted onto the recording sheet, while FIG. 22B illustrates these particles 101, 101 in a state with a given length of time having been elapsed since the corresponding inks were jetted onto the recording sheet.
In an example where the K color ink is a pigment-based ink, while the Y color ink is a dye-based ink, as shown in FIG. 22B, the particle 100 of the Y color ink penetrates into between fibers of the recording sheet faster or earlier than the particle 101 of the B color ink.
Due to the difference in penetration rate between the particles 100, 101, a portion of the particle 101 of the K color ink is brought into contact with the particle 100 of the Y color ink, and the particle 101 of the K color ink, because of a surface tension acting on the aforementioned portion thereof, is drawn toward the particle 100 of the Y color ink, resulting in color bleed causing a K color ink dot region to spread over a Y color ink dot region.
In particular, in the case where a character is printed in black on a recording sheet with its under color being selected yellow, a limitation arises that the outline of the printed character becomes indistinct due to the spread of the K color ink used for forming the black colored character over the yellow colored underground of the recording sheet. An added limitation also arises that the spread of the black color over the yellow under color is particularly noticeable, due to the contrast of the black color with the yellow color.
To overcome the above limitations, a technique is disclosed in Japanese Publication HEI 5-162339 for controlling the volume of an ink to be jetted onto a recording sheet, so that adjacent ink dots different in color are printed on the recording sheet using the corresponding inks at least one of which is reduced in volume than a standard value.